Method for the Biological Treatment of an Effluent and Associated Plant

ABSTRACT

The invention relates to a method for the biological treatment of an effluent to be treated and containing at least two forms of pollution, one of which is more easily biodegradable than the other, which comprises using a main biological treatment area in which the raw effluent is contacted with biological sludge adapted for consuming a first form of pollution that can be more easily degraded than a second form of pollution, wherein said method is characterised in that comprises collecting a fraction at least of the biological sludge which is isolated at a distance from the main biological treatment area in a so-called bioactivation area and under aeration and time conditions adapted for triggering in said fraction the development of new biological functions capable of consuming the second form of pollution, and further recycling at least a portion of said biological sludge fraction towards the main biological treatment area.

This application is a U.S. National Stage Application of PCT ApplicationNo. PCT/FR2009/000600, with an international filing date of 12 Feb.2009. Applicant claims priority based on French Patent Application No.0853416 filed 26 May 2008. The subject matter of these applications isincorporated herein.

The invention relates to a method and a device for the biologicaltreatment of polluted effluents, in particular waste water, for exampleurban or industrial waste water, implementing control of a biomasswithin a biological reactor.

As is known, the principal of a biological treatment of pollutionconsists in supplying a raw effluent loaded with pollution to apopulation of bacteria (constituting a biomass) capable of feeding onthis pollution to be treated.

It is understood that the proliferation of bacteria capable of consumingthis pollution is thus promoted naturally such that, even though thepollution is partially converted by the bacteria into nitrogen andcarbon dioxide, the biomass grows continuously, which makes it necessaryto provide for the excess biomass to be removed.

It should be specified here that sludges form during a biologicaltreatment, and that they comprise biomass, i.e. the various bacterialpopulations which have been able to proliferate by feeding on pollutioncontained in the raw effluent, and non-degraded particles of pollution.

The treatment and discharge of these sludges are becoming an importantissue, from both the environmental and the economic point of view, whichexplains why it has already been suggested that an attempt be made tocontrol biomass with a view to optimizing the process, for example byreducing the quantity of biological sludges formed.

Thus a method for the biological treatment of effluents is known,according to the document EP-1 486 465 (ONDEO), that comprises a stageof control of bacterial growth upstream of the activated sludge tank.

This document recommends the implementation of a control tank in whichthe optionally thickened sludges, obtained by clarification of the flowcoming from a biological tank, accumulate.

The redox potential of this control tank is regulated by acting on aninlet flow into this reactor of this raw effluent to be treated or on anoutlet flow of sludges from this reactor to the biological tank, so thatthis potential remains as close as possible to the equilibrium valuebetween an oxidizing state and a reducing state: it follows from thisthat reactions using oxidizing and reducing compounds are thusimplemented.

In this way, the development and bacterial growth in the control tankare apparently limited.

Moreover, a method for the treatment of waste water by fixed biologicalcultures is known, according to the document FR-2 844 786 (ONDEO), thatinvolves a step of purification and a step of reduction of theproduction of sludges, these two stages being separated.

The step of reduction of the production of sludges includes athermophilic enzymatic degradation step followed by a step of biologicaltreatment by activated sludges.

The secondary reactor is therefore heated in order to select athermophilic biomass and cause lysis resulting in the occurrence of asubstrate that is nutritious for the bacteria of the biologicaltreatment.

A method and apparatus for the biological treatment of waste water arealso known, from the document U.S. Pat. No. 5,356,537 (Thurmond et al),that involves an aeration reactor and a clarifier carrying out aseparation of the clusters of activated sludges from the rest of theliquid.

The method also involves sending a 5 to 25% fraction of the activatedsludge into an aerobic “digestion” reactor for 16 to 24 h beforereinjecting it upstream of the aeration reactor.

Nevertheless, the known methods are often limited in terms of efficiencyof the degradation of the pollution, in particular when there aredifferent chemical species present and that some are more difficult todegrade than others. Moreover, the known methods do not allow thetreated organic matter to be valorized, which is disadvantageous on theeconomic level.

The subject of the invention is to overcome these drawbacks.

To this end, the aim is a method and a device for biological treatmentimplementing an active control on the biomass so as to lead to theconsumption of as much as possible of the various types of pollutioncontained in the raw effluent and the production of the compounds ofinterest, without involving a large investment or demanding operatingconditions.

The invention thus proposes a method for the biological treatment of aneffluent to be treated containing at least two types of organicpollution, one of which is more easily biodegradable than the other,using a main zone for aerated biological treatment in which the raweffluent is brought into contact with biological sludges suitable forconsuming a first type of pollution that is easier to degrade than asecond type of pollution, the method being characterized in that atleast a fraction of the biological sludges that are isolated at adistance from the main biological treatment zone is removed, underaeration and time conditions suitable for bringing about a developmentof new biological functions in this fraction able to consume the secondtype of pollution and then at least a part of this fraction ofbiological sludges is recycled to the main biological treatment zone.

It will be appreciated that the invention involves the synergy ofseveral areas of expertise:

-   -   microbiology in order to monitor the cellular viability of the        method and the bacterial fauna established in the biological        treatment zone;    -   enzymology in order to promote certain advantageous biological        reactions.

The invention thus comprises the combination:

-   -   of a metabolic control method for the sludges within an        adjoining zone, in practice constituted by a reactor called a        bioactivation reactor, implementing a recirculation loop between        the biological treatment zone and the bioactivation zone; the        residence time of the sludges in the bioactivation reactor being        defined according to the type of the sludge of the biological        treatment zone, such an adjustment being novel per se;    -   and of a method for controlling the metabolism of the biomass in        order to degrade the particulate pollution by secretion of        specific compounds (enzymes or others) and/or by adaptation of        the biomass of the sludges; and by keeping the biomass in this        bioactivated state (i.e. with biologically modified activity)        for an appropriate time before its reinjection into the        biological treatment zone, this aspect being novel per se.

In a family of embodiments, the bioactivation zone is aerated, theresidence time of the isolated fraction of sludges being comprisedbetween 1 and 21 days.

In another family of embodiments, the bioactivation zone is anaerobic,the residence time of the fraction of isolated sludges being definedaccording to the age of the biological sludges.

An optional thickening can also be implemented. If the sludges are notthick, it is useful to increase the substrate-biomass contact surface.In all cases, it can be useful to reduce the volume of the tank. A mixercan be used to ensure a homogeneity of the sludges if they are thick.

An additional, optional, conditioning stage can be added with a view toa subsequent valorization of removed compounds of interest in the flowcoming from the bioactivation zone to the biological treatment zone,which allows the efficiency of the production of these compounds ofinterest (in particular: enzymes, biopolymers, etc.) to be increasedwhile the object of the method is centred more specifically on thispurpose.

It has been seen that the existing systems are based on cellular lysisand/or mechanical, thermal or chemical solubilization in a reactor thatis adjoining or not.

By contrast, according to the invention, the degradation of thepollution or the production of compounds of interest takes place in abiological treatment reactor (unlike the aforementioned document U.S.Pat. No. 5,356,537 in particular), preferably at ambient temperature (nothermal treatment is necessary for the selection and/or conditioning ofthe biomass) and without involving a cellular lysis (unlike the documentFR-2 844 786 in particular), by an endogenous fauna, capable ofcoexisting in the biological treatment reactor and of lasting there(unlike FR-2 844 786 in particular) and by a specific biomass in anadjoining reactor (unlike EP-1 486 465).

Thus, the bioactivation zone, owing to the fine control and command ofthe biological phenomena that occur there, allows the sludge containedin the biological treatment zone to be maintained in an optimum state,with a view to consuming, after recirculation into the biologicaltreatment reactor, the majority of the pollution, including thepollution that is difficult to biodegrade, and converting the moresignificant organic matter.

The result is a more thorough purification, or a production of compoundsof interest or a minimization of the sludges formed.

The act of diversifying the bacterial populations present in thebiological treatment zone has the advantage, for a generally moderateincrease in the biomass, of greatly reducing the part of the sludgesconstituted by pollution that is not consumed or degraded and/orproducing compounds with added value.

It may be noted that, according to the invention, the bioactivation zoneis placed downstream of the biological treatment zone and in no casereceives the raw effluent, since it is desired to induce a nutritionaldeficiency in this bioactivation zone; the metabolic control of theisolated fraction is therefore based not on the redox potential but onother parameters that it had not been normal to monitor: solublechemical oxygen demand (or COD), nitrates content, exopolysaccharidescontent, or enzymatic activities such as ATP (adenosine triphosphate).

Moreover, heating the bioactivation zone is not obligatory; there istherefore not necessarily a selection of bacteria according to thetemperature.

In addition, it is not in the bioactivation zone that the conversion ofthe pollution takes place but in the biological treatment zone itself.The activation of the isolated fraction is controlled by monitoringmeasurements of biological activities of this isolated fraction(according to the case: soluble COD content, nitrates, saccharides, inparticular exopolysaccharides contents, ATP value, etc.).

The residence time of the sludges in the bioactivation zone is adaptedto the nature of the isolated fraction of sludges and can vary from 1 to48 hours under anaerobic conditions and from 1 to 21 days under anoxicor aerobic conditions. Under anaerobic conditions, the residence timecan be fixed as a function of the age of the sludges of the mainbiological treatment zone: the older the sludges are, the longer theresidence time in the bioactivation zone is. A proportionalityrelationship between these two variables can be chosen. It should berecalled that the age of the sludges is defined by the relationshipbetween the quantity of matter present in suspension in the aerationtank and that extracted per unit of time, that is to say the residencetime of the biomass in the tank.

According to an optional and advantageous feature of the invention, theaeration and time conditions are suitable for converting the second typeof pollution into valorizable products.

Other optional features can possibly be combined with the previousfeatures.

According to an optional feature, the fraction of the biological sludgesthat is isolated is chosen between 30% and 600% of a daily production ofsludges of the main treatment zone or preferably between 30 and 300%.

The fraction of sludges removed can be defined by a predetermined ratewith respect to the production of sludges of the method in particularduring the reference period.

According to an optional feature, the aeration and time conditions aredefined as a function of the monitoring of at least one parameterpreferably directly characterizing the biological state of the fractionof isolated sludges, and preferably the state of activity of thebiomass.

The aeration and time conditions can be predefined or continuouslydefined.

According to an optional feature, this parameter is chosen from anindicator of suspended matter (or MES), a soluble or total chemicaloxygen demand, an indicator of nitrogenous species, an enzymaticactivity, a proteins indicator, a polysaccharides indicator or acomposition of the biomass.

According to an optional feature, the aeration and time conditions arechosen so as to control at least one phenomenon chosen from anutritional deficiency, a moderate inhibition, a pressure, atemperature, a pH, a change in the nature or in the concentration ofelectron acceptors.

According to an optional feature, the aeration and time conditions aresuch that a conversion of at least one type of pollution occurs in theisolated sludge fraction between the removal and the recycling.

The type of pollution which is thus converted can be the first type orthe second type.

According to an optional feature, before the recycling, at least onesubfraction that is isolated under aeration and time conditionssufficient for bringing about the development of other new metabolicfunctions capable of consuming another type of pollution is removed fromthe fraction, and at least a part of this subfraction is recycled intothe biological treatment zone.

According to an optional feature, at least one second fraction of thesludges is removed and isolated from the biological treatment zone underaeration and time conditions sufficient for bringing about thedevelopment of other new metabolic functions capable of consuming othertypes of pollution, and at least a part of this second fraction isrecycled into the biological treatment zone, the first and the secondfractions of sludges being treated in parallel.

According to an optional feature, the development of new biologicalfunctions includes a proliferation of a biological species, amodification of a distribution of a production of intracellular enzymes,a modification of a distribution of emission of exocellular enzymes or amodification of a population dynamics of a species.

According to an optional feature, a concentration treatment is appliedto the fraction before bringing about a development of new biologicalfunctions in the fraction.

According to an optional feature, the concentration treatment is applieduntil a concentration of at most 40 kg of sludge per m³ of liquid isobtained in the case where the majority of the sludges are formed ofmesophilic populations.

According to another optional feature, the aeration conditions includean oxygen concentration of less than 2 mg of O2 per litre.

The invention also proposes, for the implementation of the methoddefined above, a plant for the biological treatment of an effluent to betreated containing at least two types of matter or organic pollution,one of which is more easily biodegradable than the other, the plantcomprising a main zone for aerated biological treatment in which the raweffluent is brought into contact with biological sludges suitable forconsuming the first type of pollution that is easier to degrade than thesecond, characterized in that it comprises a removal route for at leasta fraction of the biological sludges connected to a secondary zone, thefraction being isolated at a distance from the main biological treatmentzone, under aeration and time conditions sufficient for bringing aboutthe development of new biological functions in this fraction capable ofconsuming the second type of pollution that is more difficult todegrade, and a line for recycling this fraction of biological sludges tothe main biological treatment zone.

The plant can also comprise a valorization reactor system for productsof interest, which can take the form in particular of a unit forconditioning products with a view to their valorization.

Objects, features and advantages of the invention will become apparentfrom the following description, given by way of illustrative,non-(imitative example, with reference to the attached drawings inwhich:

FIG. 1 is a block diagram of a biological treatment plant suitable forimplementing the invention,

FIG. 2 is a diagram of this plant in a particular embodiment form,

FIG. 3 is a graph showing the change over time of the total chemicaloxygen demand (reduction of the COD), of the soluble COD and of thepolysaccharides content, within the bioactivation reactor of FIG. 2,

FIG. 4 is a diagram showing the change over time of the nitrogenousforms within the bioactivation reactor of FIG. 2,

FIG. 5 is a graph showing the change over time of the content of sludgesin the biological sludge tank of FIG. 2, during two reference periods,

FIG. 6 is a graph showing the change over time of the content of sludges(volatile suspended matter MVS, suspended matter MES and dry matter MS)within the bioactivation reactor of FIG. 2,

FIG. 7 is a graph showing the change over time of the content of sludgesin the biological treatment reactor of FIG. 2, during two referenceperiods, a period of recirculation at 30% and a period of recirculationat 100%,

FIG. 8 is a graph analogous to that of FIG. 7, showing the change overtime of the content of sludges in the bioactivation reactor of FIG. 2,during two reference periods, a period of recirculation at 30% and aperiod of recirculation at 100%,

FIG. 9 is a block diagram of another plant conforming to the invention,comprising several bioactivation reactors in series,

FIG. 10 is a block diagram of yet another plant conforming to theinvention, comprising several bioactivation reactors in parallel,

FIG. 11 is a graph of the results obtained with the device of FIG. 9,

FIG. 12 is a block diagram of yet another plant conforming to theinvention, comprising a conditioning zone between the bioactivationreactor and the biological treatment reactor, and

FIG. 13 is a diagram of another plant conforming to the invention,comprising a conditioning zone at the outlet from a bioactivationreactor.

DETAILED DESCRIPTION

Two indicators are currently used for pollution. The first is aquantitative indicator indicating the distribution by mass of the maincomponents carbon/nitrogen/phosphorus. It is used to measure theparticulate organic matter (for example the bacteria), the mineralmatter (for example the sands), the dissolved salts (containing nitrogenand phosphorus), the soluble organic matter (such as proteins orpolysaccharides). The second is a qualitative indicator, concerning theassessment of levels of risk to health and the environment. It measuresendocrine disruptors and heavy metals for example.

FIG. 1 represents a biological treatment plant 10 comprising:

-   -   an inlet route 11 for raw effluent, such as waste water,    -   a main biological treatment reactor 12, here provided with an        air inlet 13 due to which the reactor 12 is an aerated reactor        (continuous or sequenced aeration, in this case with the        presence of temporal phases suitable for bringing about an        aerobic treatment for carbon and ammonia, then an anoxic        treatment for nitrates, then an anaerobic treatment for        phosphorus),    -   a concentrator 14 connected, here in the lower part, to an        outlet of the biological treatment reactor 12,    -   a bioactivation reactor 15, here aerated due to an air inlet 16,        connected to the outlet of the concentration reactor,    -   a recirculation line for bioactivated sludges 17, connected        between an outlet, here in the lower part, of the bioactivation        reactor 15, and an inlet, here in the lower part, of the        biological treatment reactor 12—the recirculation line 17        advantageously comprises a pump 18,    -   a discharge line 19 for excess sludges connected to an outlet of        the biological treatment reactor and comprising a pump 20,    -   an outlet route for treated water 21, connected to an outlet,        here in the upper part, of the biological treatment reactor, and    -   an outlet route 22, connected to an outlet of the bioactivation        reactor, here in the upper part and able to reach, on the one        hand, the biological treatment reactor and/or, on the other        hand, an outlet of the plant.

Such a plant allows a method for the biological treatment of a raweffluent to be implemented, capable of controlling the metabolism of thebiomass, principally comprising the following steps:

a) an effluent to be treated entering by route 11 is brought intocontact with, principally, free cultures forming part of the biologicalsludges, in at least one tank or biological treatment reactor 12;

b) a fraction of the sludges of the biological treatment reactor issent, at a defined rate, to one (or even several) bioactivationreactor(s) 15 which is (or are) isolated vis-à-vis the reactor 12 andwhich can be individually aerated, or micro-aerated (i.e. aerated with abubbling of micrometric size), or anaerobic, so as to perform biologicaladaptations of the state of the biomasses of this fraction under theinfluence of various factors (alone or combined) such as a nutritionaldeficiency, a moderate inhibition (i.e. a moderate nutritionaldeficiency), the pressure, the temperature, the pH, the change inelectron acceptor (this list not being limiting),

c) for each bioactivation reactor, a recirculation loop 17 ensures thecoupling to the biological treatment reactor 12, and allows between 30and 300% of the bioactivated sludges to be sent back to the biologicaltreatment reactor 12.

It is specified that the recirculation rate is defined with respect tothe reference production of sludge, measured at the activated sludgereactor blow off level.

The residence time of the sludges in the bioactivation reactor 15 iscontrolled by the measurement of parameters representing the biologicalstate of the sludge which is isolated there (suspended matter,nitrogenous forms, soluble and total COD, enzymatic activity, proteins,polysaccharides, composition of the biomass, etc.) and is specific toeach type of sludge.

The recirculation rate, specific to the treatment in each bioactivationreactor, is a function of the biological state of the biological sludgeand the bioactivated sludge.

A tank, situated after the bioactivation zone 15 but before the returnto the biological sludge tank 12, can be added (see FIG. 12), in orderto allow the state of the biomass (suitable biological species, specificenzymes, production of products of interest) to be preserved in a statesuch that their return to the biological treatment reactor allows a morethorough degradation of the organic matter and/or the compounds ofinterest produced to be conditioned in order to be able to valorize themto another reactor system.

A prior stage of thickening the excess sludges is advantageously carriedout in zone 14 by any means allowing the thickening of the sludge (at amaximum of 40 kg/m³ for mesophilic populations). The thickening can bedone, for example, using a membranous technique, a draining table, astatic thickener, a rotary drum, etc.

The thickening, which is optional, serves on the one hand, in the caseof non-thickened sludges, to increase the substrate-biomass contactsurface and on the other hand to reduce the volume of the tank. A mixercan ensure a homogeneity in the case of thickened sludges, but oxygentransfer is no longer effective above a certain threshold (40 kg/m³).

The bioactivation reactor can also function with various families ofbacteria such as psychrophiles or thermophiles, for example, by adaptingthe operating conditions of the reactor.

Generally, the invention can be implemented with any method for thebiological treatment of polluted effluents and waste. In particular, thebiological treatment can be carried out using conventional methodseliminating carbon, ammonium or nitrates, for example activated sludges,MBRs (membrane bioreactors), or MBBRs (moving bed bioreactors).

An implementation was carried out by way of example over 21 days. Theactivated sludges (in the case of the example) are concentrated between4 and 40 g/L by settling (this choice is not imperative) and placed in acontinuously aerated column (acting as bioactivation zone) in order topromote bacterial growth without introducing nutrients.

The reduced introduction of nutrients to the bioactivation reactor,because of its isolation, brings the bacteria into a state ofnutritional deficiency that creates a state of adaptation of thebiomass.

Monitoring the biological parameters and the concentration of sludge wascarried out. The monitoring, in the bioactivation reactor, is performedon the basis of measurements of the soluble COD and nitrates, to whichother parameters can be added, such as the NH₄ ⁺ ion, proteins,exopolysaccharides or cellular activity which allow a continuous andin-situ analysis and therefore a fine control (or command).

From a time comprised between 1 and 21 days, a specific biological stateof the biomass that is very nearly constant, i.e. a plateau, isobserved.

When in operation, the bioactivation reactor 15 is controlled in orderto function permanently under conditions equivalent to the point ofreaching the plateau so that the degradation of the polluting mattertakes place after the recirculation into the biological tank fortreating the effluents.

In other words, within the isolated fraction of sludges in thebioactivation reactor the appearance of bacteria is favoured which arecapable of degrading at least one of the types of pollution present asnot spontaneously degraded in the biological treatment reactor.

Moreover, it is advantageous not to allow this new bacterial species todevelop within the bioactivation reactor, but to send it to feed in thebiological treatment reactor.

The thickened and activated sludges are recirculated into the upstreambiological treatment reactor in order to increase the enzymatic activitywithin the biological reactor of the effluents and to allow thesolubilization of the pollution that is difficult to biodegrade thusreducing the production of sludges of the system and/or thus increasingthe production of compounds of interest.

The recirculated volume is chosen according to the state of the biomass.The residence time in the bioactivation zone is predetermined dependingon the type of sludge.

As indicated above, an additional conditioning stage can be added with aview to conditioning the compounds of interest before recirculationand/or valorization to another reactor system. Compounds of interest canbe activated carbon, enzymes (for example proteases, carbohydrases,lipases or oxidases), bioplastics, biopesticides and biogases, amongothers.

Example 1 Mono-Bioactivation Method

With reference to FIG. 2, an embodiment example of the method accordingto the invention involving a single bioactivation (mono-bioactivationmethod) is shown.

The treated water is waste water from an urban environment containing150 mg/L of MES, a total COD of 500 mg/L, a soluble COD of 250 mg/L, anitrogen concentration (ammonia equivalent) of 35 mg/L, a TN (totalnitrogen) level of 50 mg/L, and a phosphorus concentration (phosphateequivalent) of 6 mg/L.

Screened waste water 61 is introduced in sequence or continuously intoan activated sludge tank 62. For example, it is introduced with acontinuous flow of 130 L/h. The activated sludge tank has a volume of1100 L.

When the tank 62 is not being fed by a pump, the water returns in aclosed loop to a storage tank. A stirrer allows the inlet effluents tobe homogenized with the activated sludge present but need not break upthe flocs. A fine bubble aeration aerates the mixture in order to allowbacterial growth as well as the processes of decarbonation andnitrification/denitrification.

The sludge between 3 and 5 g/L is discharged to a bioactivation reactor64, with a volume comprised between 80 and 350 L. The transfer of thissludge from the activated sludge tank to the bioactivation reactor isnoted by reference 63. The flow transferred to the bioactivation reactoris from 44 to 264 L/d. Excess sludges 66 also leave the activated sludgetank. The rate of treatment of the sludges is from 30 to 600%.

Flat membranes play the role of clarifier, i.e. separator of the sludgesfrom the clean water. The extracted permeate is analysed to find out itsnitrates content in order to regulate the sequencednitrification/denitritication. An aeration system allows clogging of themembranes to be avoided.

A volume of activated sludges is introduced in a sequenced fashionwithin the bioactivation reactor. The sludge is thickened up to 20-25g/L by two submerged membrane modules.

The extracted permeate 67 is analysed to find out its nitrates contentin order to regulate the sequenced nitrification/denitritication. Theoutlet flow is 110 L/h and is in sequenced mode (8 minutes out of 10),which avoids clogging the membranes. A large bubble aeration at thelevel of the membranes allows their clogging to be avoided and a finebubble aeration at the bottom of the tank allows bacterial growth.

The imposed conditions (biological residence time) depend on the natureof the sludge of the activated sludge tank and allow the enzymaticactivity to increase. In the described example, this method isimplemented such that the biological residence time (i.e. the residencetime in the bioactivation tank 64) is preferably 7 days.

A 20-25 g/L sludge volume (reference 65) is recirculated daily to theactivated sludge tank by a positive displacement pump, so as to degradethe particulate COD and therefore to reduce the production of sludges.

In FIG. 3, the total COD (Dt), the soluble COD (Ds) and thepolysaccharides (P) of the sludge placed in aerobic stabilization aremonitored as a function of time.

This makes it possible to find out the duration of the plateau (zonewhere the COD no longer changes, and where there is a selection and a“bioactivation of the flora”); and therefore the time needed for theadaptation of the bacteria to the medium: 3 to 9 days in the aboveexample, where the soluble COD passes from 50 mg/L to approximately 450mg/L and the polysaccharides from 5 to approximately 150 mg/L.

If the COD increases, there is solubilization. Thus, the matter isconverted and free in the sludge of the soluble pollution which istherefore easier to assimilate. When the plateau of total COD isreached, the bioactivation is at its maximum. The enzymes or species putin place allow the matter to be converted.

Similarly, in FIG. 4, the total nitrogen (Nt), the soluble nitrogen (Ns)as well as the nitrates (Ni) were monitored as a function of time.

The same plateau that starts from the 3^(rd) day is found: increase inthe nitrates from 2 to 100 mg/L and therefore parallel to the solublenitrogen but not to the total nitrogen which remains stable atapproximately 600 mg/L.

The measurements thus allow a change in the nitrogenous forms at thesame time as the solubilization of the COD.

The method involves a stabilized biological operation taking intoconsideration a repetition of the cycle of removing a fraction of thesludges, its isolation, then its reinjection according to a givenrecirculation rate.

FIG. 5 represents the monitoring of the content of sludges in theactivated sludge tank (the scale of the y-axis being logarithmic). TheMES (suspended matter) concentration of the activated sludge is stableat about 5 g/L. The same is true of the MS (dry matter) and MVS(volatile suspended matter) concentrations. In this figure, tworeference periods occur, i.e. periods during which the activated sludgetank functions in a stable pattern.

FIG. 6 represents the change in the content of sludges in thebioactivation reactor (there is a single reference period because thebioactivation was started once the activated sludge had beenstabilized).

The content (representing the various matter contained in these sludges)is stable. The MES concentration is 18 g/L, the MS concentration is 20g/L and the MVS concentration is 15 g/L. They are obtained with athickening process, and are very satisfactory. The sludge volume isreduced, and the aeration is nevertheless satisfactory.

Recirculation is then established.

FIGS. 7 and 8 respectively represent the change in the sludge in theactivated sludge tank (AS, FIG. 7) and in the bioactivation zone (BI,FIG. 8) in different recirculation phases.

Over the first weeks, at a reduced recirculation rate (30% by mass, zoneR), the results show a stability in the concentrations of the two tanks:the activated sludge in the main tank is at approximately 6 g/L and thebioactivated sludge in the bioactivation tank at 20 g/L.

During the increase in the recirculation rate to 100% (zone E for a highrecirculation rate), a significant drop in the content of sludges in thetwo tanks can be noted, after only two weeks.

Thus, a reduction in the content of matter in the tanks (4.5 g/L and 16g/L respectively) is obtained, hence a reduction in the production ofsludges at the outlet of the plant.

Example 2 Implementation of the Method with Tanks in Series

FIG. 9 diagrammatically represents a plant 210 similar to that of FIG.1, but comprising several bioactivation reactors in series, each of themimposing different conditions in order to promote different enzymaticreactions and therefore enrich the biodiversity. Moreover, the productor products of the reactions of an upstream reactor are then used assubstrates for the reactions of a downstream reactor. In the exampledescribed, the carbon is converted into volatile fatty acids, and theseare converted to methane or PHA biopolymers.

The elements similar to those of FIG. 1 are indicated by a numberderived from that of FIG. 1 by adding the number 200, the reactors beingreferenced 215A, 215B and 215C.

It can be noted that there is a reinjection (or recirculation) line 217for each bioactivation reactor. It is a concentrated outlet (at thebottom, containing bioactivated sludges). For each reactor, there isalso a clear outlet (at the top), the flow of which can be partiallyrecirculated to the reactor 212 (route 222) if it is desired to controlthe residence time of certain soluble fractions in a different way tothe residence time of the activated sludges. Finally, an outlet route tooutside the plant is also provided for each reactor (towards thebottom).

In a variant, not represented, the outlet flow of the reactors 215A and215B is divided between the following reactor (215B and 215Crespectively) and a common reinjection line 217; which can allow theproportions transmitted to the following reactor and reinjection to bevaried.

Different parameters are also monitored depending on the matter to bedegraded or produced. An assembly of tanks in series allows chainreactions to be carried out, each tank carrying out a link in the chainof reaction.

The final yield is higher. In the example described, 0.6 g of VFA pergram of COD, then 0.65 g of methane per gram of carbon are obtained. Inanother example, 0.6 g of volatile fatty acid per gram of COD, then 0.11g of PHA biopolymers per gram of COD are obtained. Without treatment inseries, the yield would be divided by a factor of two, approximately.

Example 3 Implementation of the Method with Tanks in Parallel

FIG. 10 represents a plant 110 similar to that of FIG. 1 except that,instead of a single bioactivation reactor, there are several (115A,115B, 115C), mounted in parallel, each of them being able to imposedifferent conditions in order to promote several different enzymaticreactions and therefore enrich the biodiversity, so as to allow severaldifferent products to be obtained, each being able to be valorized. Forexample, in the case of the conversion of carbonaceous matter, thevolatile fatty acids produced can be extracted, without being convertedto PHA biopolymers.

In this FIG. 10, the elements similar to those of FIG. 1 are denoted bythe reference numbers derived from those of this FIG. 1 by adding thenumber 100; the various bioactivation reactors are referenced 115A, 115Band 115C.

In the example schematized here, the recirculation of all or some of thecontent of these bioactivation reactors could be ensured by the sameline, but there is one reinjection line for each reactor 115A to 115C,the lines being numbered 118A, 118B, 118C. An outlet route to outsidethe plant is provided for each reactor, on the right of the diagram.

By way of example, the reactor 115A is conditioned so as to bring aboutthe occurrence of a biological species capable of consuming thesubstrates that are difficult to degrade A, the reactor 115B isconditioned so as to bring about the appearance of another biologicalspecies capable of consuming the substrates that are difficult todegrade B and the reactor 115C is conditioned so as to bring about thedevelopment of a biological species capable of consuming the substratesthat are difficult to degrade C.

This assembly makes it possible to proceed with degradations underdifferent bioactivation conditions in the different tanks.

Different parameters are monitored depending on the matter to bedegraded or produced. For example, proteins or fibres can be monitoredif it is desired to degrade such substrates. The reduction of dissolvedoxygen, or the occurrence of volatile fatty acids, or other parameters,can also be monitored.

In the example, described in the first reactor 115A, volatile fattyacids are produced in order to then be extracted from the method.

In the second reactor 115B, PHA biopolymers are produced and alsoextracted from the method.

In the third reactor, the environmental conditions are adjusted topromote enzymatic activity (for example proteases) and to degrade thematter. In this reactor, the degradation of the pollution is promoted.

The following numerical values are obtained: volatile fatty acids yield0.6 g per gram of COD; biopolymers yield 0.11 g per gram of COD;proteases yield 0.01 g per gram of carbon. At equilibrium, i.e. in theexploitation phase, the production obtained is 230 g per day of PHAbiopolymers and 1250 g per day of volatile fatty acids. 2060 g ofproteases are recirculated per day out in order to promote thedegradation of the matter in the activated sludge tank.

FIG. 11 presents the yields of PHA biopolymers, volatile fatty acids andproteases obtained with and without using the method, the values on they-axis being in grams per day. The effect of the method is clearlyvisible.

Example 4 Implementation of the Method with Conditioning

FIG. 12 represents a plant 310 similar to that of FIG. 1 except that anadditional conditioning stage, reference number 330, that is notobligatory, is added on the reinjection line between the outlet of thebioactivation reactor 315 and the inlet of the biological treatmentreactor 312.

The object of this conditioning stage is the conditioning of thecompounds of interest before recirculation and/or valorization, with theaim of increasing the efficiency of the production of compounds ofinterest (enzymes, biopolymers, etc.).

In FIG. 12, elements similar to those of FIG. 1 are given referencenumbers derived from those of FIG. 1 by adding the number 300.

Example 5 Another Implementation of the Method with Conditioning

FIG. 13 represents a similar plant 410 which, in this particular case,involves a micro-aerated or non-aerated bioactivation reactor 415producing volatile fatty acids by acidogenesis, according to afermentation process.

This reactor 415 is installed in communication with an aeratedbiological treatment reactor 412. The waste water inlet is numbered 411,and a route for supplying the bioactivation reactor by the biologicaltreatment reactor is referenced 414, and involves a thickening process,or does not. The excess sludges leave the biological treatment reactorby the route 420, and the treated water by the route 421.

In the context of this particular example, a separation method,reference number 408, is also implemented, followed by a method ofprecipitation of nitrogen and/or phosphorus. These two stages areoptional.

A bioactivation reactor for aerated conditioning, having referencenumber 409 and comprising two tanks, is also implemented. At the outletof the first tank of this reactor, a production of microorganisms 430capable of accumulating biopolymers, by bioaugmentation, i.e.bio-organism enrichment is obtained. At the outlet of the second tank, aproduction of biopolymers 440 is obtained.

1-18. (canceled)
 19. A method for the biological treatment of aneffluent containing two or more types of organic pollution wherein afirst type of organic pollution is easier to degrade than a second typeof organic pollution, comprising: degrading the easier to degrade firsttype of pollution by bringing the effluent into contact with biologicalsludge capable of consuming the easier to degrade first type ofpollution in a main aerated biological treatment zone; removing at leasta fraction of the biological sludge from the main biological treatmentzone and isolating the removed sludge at a distance from the mainbiological treatment zone in a bioactivation zone, wherein the sludge insaid bioactivation zone is treated by subjecting the sludge to aerationand residency time conditions that gives rise to the development of newbiological functions in the removed sludge such that the removed sludgeis capable of biologically degrading the more difficult to degradesecond type of pollution; recycling at least a fraction of the removedbiological sludge comprising the new biological functions to the mainbiological treatment zone; and degrading the more difficult to degradesecond type of pollution utilizing at least a portion of the sludgetreated in the bioactivation zone.
 20. The method according to claim 19,wherein the bioactivation zone is aerated and the residence time of theremoved sludge is between 1 and 21 days.
 21. The method according toclaim 19, wherein the bioactivation zone is anaerobic and the residencetime of the removed sludge is a function of the age of the biologicalsludge.
 22. The method according to claim 19, wherein the amount ofbiological sludge that is removed from the main biological treatmentzone is between 30% and 600% of a daily production of sludge in the mainbiological treatment zone.
 23. The method according to claim 19, whereinthe aeration and time conditions in the bioactivation zone are definedas a function of the biological state of the removed sludge, whereinsuch biological state is monitored by measuring one or more parametersrepresentative of one or more biological functions, and said aerationand residency time conditions are adjusted periodically so as tomaintain or change said biological functions in said bioactivation zone.24. The method according to claim 23, wherein the one or more parametersis selected from suspended matter (or MES), soluble or total chemicaloxygen demand, nitrogenous species, enzymatic activity, protein content,polysaccharides content, or biomass composition.
 25. The methodaccording to claim 19, wherein the aeration and time conditions arechosen so as to maintain or change at least one phenomenon selected froma nutritional deficiency, a moderate inhibition, a pressure, atemperature, a pH, or the nature or concentration of electron acceptors.26. The method according to claim 19, wherein the aeration and timeconditions are such that at least one type of pollution is degraded bythe removed sludge after removal of the sludge from the biologicaltreatment zone and before recycling.
 27. The method according to claim19, wherein the aeration and time conditions are such that conditioningof a valorizable part of the removed sludge is performed after removalfrom the biological treatment zone and before recycling.
 28. The methodaccording to claim 19, wherein before the recycling of the removedsludge, at least one subfraction of the removed sludge is subjected toaeration and time conditions sufficient for bringing about thedevelopment of other new metabolic functions capable of consuming one ormore further types of pollution, and at least a part of the subfractionis recycled to the biological treatment zone.
 29. The method accordingto claim 19, wherein at least one additional fraction of biologicalsludge is removed and isolated from the biological treatment zone underaeration and residency time conditions sufficient for bringing about thedevelopment of other new metabolic functions capable of consuming one ormore further types of pollution, and at least a part of this additionalfraction is recycled to the biological treatment zone, the removedsludge and the additional fraction of sludge being treated in parallelbioactivation zones.
 30. The method of claim 19, wherein the developmentof new biological functions includes a proliferation of a biologicalspecies, a modification of a distribution of a production ofintracellular enzymes, a modification of a distribution of emission ofexocellular enzymes or a modification of a population dynamics of aspecies.
 31. The method according to claim 19, wherein a concentrationtreatment is applied to the removed sludge before bringing about thedevelopment of new biological functions in the removed sludge.
 32. Themethod according to claim 31, wherein the removed sludge is concentratedto at most 40 kg of sludge per m³ of liquid when the majority of thebiomass in the removed sludge is mesophilic bacterial populations. 33.The method of claim 19 including maintaining the oxygen concentration inthe bioactivation zone at less than 2 mg/l.
 34. The method of claim 19wherein the aeration and time conditions imposed in the bioactivationzone gives rise to a biomass that degrades the more difficult to degradesecond type of pollution.
 35. A wastewater treatment system for treatingan effluent containing two or more types of organic pollution includinga first type of organic pollution that is relatively easy to degrade anda second type of organic pollution that is relatively difficult todegrade, the wastewater treatment system comprising: a main aeratedbiological treatment zone for receiving the effluent to be treated andwherein the main aerated biological treatment zone is adapted to containactivated sludge where the activated sludge is effective to degrade thefirst type of organic pollution in the main aerated biological treatmentzone; a bioactivation zone isolated from the main aerated biologicaltreatment zone; conduit means for directing a fraction of the activatedsludge from the main aerated biological treatment zone to thebioactivation zone; the bioactivation zone adapted to condition thefraction of activated sludge by subjecting the fraction of activatedsludge to varying aeration and residency time conditions to producebiological species in the bioactivation zone that are capable ofdegrading the second type of organic pollution in the effluent; andmeans for recycling the conditioned fraction of activated sludge fromthe bioactivation zone to the main aerated biological treatment zonewhere the biological species produced in the bioactivation zone areeffective to degrade the second type of organic pollution in theeffluent.
 36. The wastewater treatment system of claim 35 including asludge thickening zone disposed between the main aerated biologicaltreatment zone and the bioactivation zone for thickening the fraction ofactivated sludge prior to the fraction of activated sludge reaching thebioactivation zone.
 37. The wastewater treatment system of claim 35wherein there is provided a plurality of bioactivation zones disposed inseries relationship.
 38. The wastewater treatment system of claim 35wherein the wastewater treatment system includes a plurality ofbioactivation zones and where the bioactivation zones are disposed inparallel relationship and wherein there is means for recycling theconditioned activated sludge from each of the bioactivation zones to themain aerated biological treatment zone.